University researchers are studying why suspected wheat stem sawflies are being found again this year in Nebraska corn, previously thought to be a non-host. Major yield loss is not expected in corn from this pest.

Ag professionals across central and eastern Nebraska are reporting insect damage to corn following rye and wheat cover crops, likely from the wheat stem maggot. A recent field survey found stand losses in fields ranged from 2%-30% on a whole-field basis.

Figure 1. "Cross-banding" on emerged corn at SCAL planted on April 17, 2017. Leaves were encased in the coleoptile below ground during the extreme dip in air and soil temperatures. Emergence occurred between May 5 and 10 and was about 50% May 10. Expect plant-to-plant variation in emergence, growth, and development with early-planted corn. (SCAL, May 10, 2017. Photos by Roger Elmore)

Early-planted corn at the university's South Central Ag Lab was not emerged during the late-April cold snap, but upon emergence displayed symptoms of “cross-banding”: yellow to pale green, horizontal bands ― perpendicular to the leaf midribs. These often appear in a similar position on other seedlings and at about the same height above ground on different leaves.

Palmer amaranth has not been confirmed in conservation plantings in Nebraska; however, the identification and occurrence of Palmer amaranth in CRP fields in Iowa has raised concerns among weed scientists and growers about its spread into conservation plantings in Nebraska and offer some suggestions for growers.

Figure 1. (left) Yellow corn displaying damage from last week’s frost. Eighty to ninety percent of plants in this area of the field will likely recover, thus replanting would not be justified. Figure 2. Plant displaying frost injury. Both in Lancaster County, May 4, 2017. (Photos by Roger Elmore)

Considering whether your corn should be replanted? The authors look at types of plant damage at early growth stages and the effect on potential yield. It includes a table of relative yield potential of corn by planting date and population.

Early-season freeze damage results in a range of potential yield impacts. Severe damage is often limited to low-lying areas within a field because cool air is heavier than warm air. Early season survival of corn plants is attributed to growing-point protection below the soil surface; however, a hard frost can penetrate the ground and kill plants. Regrowth of corn following freeze damage is often impeded by dead leaf tissue that can entrap new leaves.